In recent years, a DVD (Digital Versatile Disc) is widely used as an information recording medium for recording/reproducing data, such as video data, audio data, computer data, and the like. The DVD comes in different types: in addition to the DVD used exclusively for reproduction, the DVD-R (recordable) which uses an organic coloring material in the recording layer thereof to allow writing-once-reading-many, the DVD-RW (re-recordable) which uses a phase change material in the recording layer thereof to allow rewriting many times, and the like.
While there is a demand for a capability of recording/reproducing by light beams of wave range shorter than 635 nm so as to cope with higher density, the conventional write-once-read-many optical disc has been unable to fully realize characteristics of the optical disc.
In addition, various optical discs of write-once type are reported, for example, one of which has a recording layer to be penetrated by the irradiation of a laser beam to have a hole, in another of which a bubble cavity in a recording layer is formed by the irradiation of a laser beam, another of which has a recording layer to have a protuberance, in further another of which a heat decomposable substance is dispersed in the recording layer by the irradiation of a laser beam. These conventional recording methods have a problem in that it is difficult to control the size and edge of a minute recorded mark formed on the recording layer with a high density recording. In other words, as shown in FIG. 16, the recorded mark is formed so as to spread out a guide groove during the recording.
Further, in the case of the write-once-read-many disc, rewriting is not allowed on an area once recorded. This increases consumption of the discs. The effects on the environment due to the dumping of the discs should be considered, because some discs may contain materials which are considered to be deleterious under “a law concerning promotion of improvements in grasp of the amount of a specific chemical material discharged to the environment, and in the control thereof or the like”, i.e., PRTR (Pollutant Release and Transfer Register) law.